The present invention relates to a valve.
More specifically, the invention relates to a hydraulic valve.
Still more particularly, the present invention relates to a hydraulic safety valve which is particularly--although not exclusively--suited for controlling safety functions in presses.
Valves of this type, when used on mechanical presses, are employed e.g. to control the brake and coupling of the press so that, should a press malfunction occur, the press cannot operate in an uncontrolled manner and cause a hazard to operating personnel. For safety reasons, this type of valve has two distinct control sections so that, in the event of malfunction of one of the sections, the other section will still assure proper braking of the press. The operation of the two sections is cyclically monitored by electrical circuits which, when they determine that one of the sections has malfunctioned, shut down the press since the valve then no longer provides the required safety redundancy.
A problem with this prior art approach is that the required electrical circuitry is quite complicated and, hence, rather expensive. Moreover, such circuitry is itself liable to malfunction which may pose safety hazards or at least disadvantageously influence the operation of the press.